Strain gauge, force sensor and interventional medical catheter

ABSTRACT

A strain gauge includes: a substrate; a transverse sensitive grid arranged on the substrate; and at least two non-transverse sensitive grids arranged on the substrate so as to be located on opposite sides of the transverse sensitive grid both electrically connected to the transverse sensitive grid. The two non-transverse sensitive grids are connected to each other by a connection and share a common ground lead and a common ground interface. One end of the ground lead is connected to the connection at the middle thereof. The other end of the ground lead is connected to the ground interface. The two non-transverse sensitive grids have equal resistances and are connected to ends of two respective non-ground leads having equal resistances. The other ends of the two non-ground leads are connected to two respective non-ground interfaces.

TECHNICAL FIELD

The present invention relates to the technical field of medicalinstruments and, more specifically, to a strain gauge, a force sensorand an interventional medical catheter.

BACKGROUND

A strain gauge is generally constructed by attaching a metallicsensitive grid onto a plastic membrane substrate. The metallic sensitivegrid is formed by a thin conductive wire arranged into a zigzag patternof parallel lines. When the strain gauge is stretched, the sensitivegrid will become narrower and longer, which increases its electricalresistance. When the strain gauge is compressed, the sensitive grid willbroaden and shorten, which decreases its electrical resistance. Aninterventional catheter is usually provided, at its distal end, with aforce sensor for detecting how the catheter contacts tissue in the body.Strain gauges can be used to produce such sensors. More specifically, astrain gauge may be attached to a circumferential wall of an elastictube arranged in the vicinity of an electrode at the distal end. Whenthe electrode comes into contact with tissue in the body, the cathetermay deform and in turn cause deformation of the elastic tube, which mayelongate or shorten the sensitive grid of the strain gauge, leading to achange in its resistance. In this way, force measurement is madepossible.

At present, commonly used commercially available resistive strain gaugestypically have only one longitudinally arranged sensitive gridconsisting of a wire with a relatively large circumferential surfacearea. The applicant has ever proposed a compact strain gauge composed ofa substrate and a plurality of longitudinal sensitive grids arranged onthe substrate. However, during practical use of this strain gauge, theapplicant has found that, it has to be pre-heated for a period of time(about from 5 to 6 minutes) before it attains a stable conditionsuitable for pressure measurement. This may extend a surgical procedureand cause inconvenience of use.

SUMMARY OF THE INVENTION

In view of the above-described shortcomings of the prior art, it is anobject of the present invention to provide a strain gauge, a forcesensor and an interventional medical catheter. The strain gauge can bestabilized very rapidly, overcoming the problem of inconvenient useassociated with the existing strain gauge caused by a required period oftime for preheating.

To this end, the strain gauge provided in the present inventioncomprises:

-   -   a substrate;    -   a transverse sensitive grid arranged on the substrate; and    -   at least two non-transverse sensitive grids both arranged on the        substrate so as to be located on opposite sides of the        transverse sensitive grid and both electrically connected to the        transverse sensitive grid,    -   wherein the two non-transverse sensitive grids are connected to        each other by a transverse connection and share a common ground        lead and a common ground interface, one end of the ground lead        connected to the transverse connection at the middle thereof,        the other end of the ground lead connected to the ground        interface, the two non-transverse sensitive grids having equal        resistances and connected to ends of two respective non-ground        leads having equal resistances, the other ends of the two        non-ground leads connected to two respective non-ground        interfaces.

Optionally, in the strain gauge, the substrate may define a firstdirection and a second direction, wherein the first direction is one ofa lengthwise direction and a widthwise direction of the substrate, andthe second direction is the other of the lengthwise and widthwisedirections of the substrate.

Optionally, in the strain gauge, the two non-transverse sensitive gridsmay be arranged in symmetry and each long a direction inclined from thefirst direction at a predetermined angle, with the transverse sensitivegrid being arranged along the second direction.

Optionally, in the strain gauge, the two non-transverse sensitive gridsmay be longitudinal sensitive grids which are arranged side by side andaligned with each other along the first direction, with the transversesensitive grid being arranged along the second direction, wherein gridwidths of the longitudinal sensitive grids are aligned with a gridlength of the transverse sensitive grid, or grid lengths of thelongitudinal sensitive grids are aligned with a grid width of thetransverse sensitive grid.

Optionally, in the strain gauge, a grid width of each of the sensitivegrids may be equal to a grid length thereof, wherein the grid-likestructures in the sensitive grids are all identical.

Optionally, in the strain gauge, the transverse sensitive grid may beelectrically connected to the two non-transverse sensitive grids throughthe transverse connection, wherein the transverse sensitive grid and thetwo non-transverse sensitive grids share the common ground lead and thecommon ground interface.

Optionally, in the strain gauge, the transverse sensitive grid maycomprise transverse wire segments, which are connected to the transverseconnection at a location close to the middle of the transverseconnection.

Optionally, in the strain gauge, the ground lead may comprise atransverse segment and a longitudinal segment, the transverse segmentconnected to the transverse connection at the middle thereof, thelongitudinal segment connected to the transverse segment at one end andto the ground interface at the other end.

Optionally, in the strain gauge, the transverse sensitive grid maycomprise transverse wire segments arranged in parallel to the transversesegment and perpendicular to the longitudinal segment.

Optionally, in the strain gauge, the two non-transverse sensitive gridsmay include a first non-transverse sensitive grid and a secondnon-transverse sensitive grid, which are connected to a first non-groundlead and a second non-ground lead, respectively, wherein one end of thetransverse sensitive grid is connected to the transverse connection, andthe other end of the transverse sensitive grid is connected to a thirdnon-ground lead, wherein the first, second and third non-ground leadshave equal resistances, and wherein the third non-ground lead isconnected to a third non-ground interface.

The force sensor provided in the present invention comprises anelastomer and strain gauges as defined in any of the above paragraphs,which are provided on the elastomer.

Optionally, in the force sensor, the elastomer may be provided thereinwith a plurality of through-slots extending circumferentially around theelastomer, each of which is provided at each end thereof with an axialslot extending along an axis of the elastomer.

Optionally, in the force sensor, the axial slots may each have a lengththat is not less than the grid width or grid length of each sensitivegrid in each strain gauge, or not less than a width of each sensitivegrid along the axial of the elastomer.

The interventional medical catheter provided in the present inventioncomprises a distal catheter end, at which a force sensor as defined inany of the above paragraphs is provided.

Compared to the prior art, the strain gauge provided in the presentinvention includes a substrate, one transverse sensitive grid arrangedon the substrate, and two non-transverse sensitive grids both arrangedon the substrate so as to be located on opposite sides of the transversesensitive grid and both electrically connected to the transversesensitive grid, wherein the two non-transverse sensitive grids areconnected to each other by a transverse connection and share a commonground lead and a common ground interface, wherein one end of the groundlead is connected to the transverse connection at the middle thereof,and the other end of the ground lead is connected to the groundinterface, wherein the two non-transverse sensitive grids have equalresistances and are connected to ends of two respective non-ground leadshaving equal resistances, and wherein the other ends of the twonon-ground leads are connected to two respective non-ground interfaces.This design allows higher accuracy, faster attainment of a stablecondition when connected in a circuit and enhanced interferencerejection performance of the strain gauge. According to the presentinvention, through employing the strain gauge in the force sensor andthe interventional catheter, the period of time for preheating thecatheter in the human body can be effectively shortened, and thecomplexity and risk of a surgical procedure to be performed by aphysician and a patient's suffering can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor actions. The sizes and relative positions of the elements in thedrawings are not necessarily drawn to scale. For example, the forms ofthe various elements and angles are not necessarily drawn to scale, andsome of these elements are enlarged and located arbitrarily to improvethe understanding of the drawing. In addition, the particular forms ofthe elements as drawn do not intend to convey any information concerningthe real shape of the particular elements and only have been selected tofacilitate its recognition in the drawings, wherein:

FIG. 1 is a schematic diagram illustrating the structure of an existingstrain gauge according to an embodiment of prior art;

FIG. 2 is a schematic diagram illustrating the structure of the existingstrain gauge according to another embodiment of prior art;

FIG. 3 is a diagram showing a half Wheatstone bridge circuit of thestrain gauge of FIG. 2 ;

FIG. 4 shows an isometric view of a strain gauge according to anembodiment of the present invention;

FIG. 5 shows a bottom view of the strain gauge of FIG. 4 ;

FIG. 6 shows an isometric view of a strain gauge according to anotherembodiment of the present invention;

FIG. 7 shows a top view of the strain gauge of FIG. 6 ;

FIG. 8 is a schematic diagram illustrating the structure of a forcesensor according to an embodiment of the present invention, which isbeing attached to an electrode;

FIG. 9 is an elevation view of an elastomer according to an embodimentof the present invention, on which two strain gauges are evenlydistributed;

FIG. 10 is a perspective view of an elastomer according to an embodimentof the present invention, on which two strain gauges are evenlydistributed; and

FIG. 11 shows a top view of an electrode disposed at a distal catheterend of an interventional medical catheter according to an embodiment ofthe present invention.

DETAILED DESCRIPTION

Objects, aspects and advantages of the present invention will becomemore clear and apparent from the following more detailed description ofembodiments thereof, which is to be read in connection with theaccompanying drawings. It is to be understood that the specificembodiments described herein are merely intended to explain theinvention, rather than limit the invention.

As used hereinabove, the terms “proximal” and “distal” describe relativeorientations, relative positions and directions between elements oractions, as viewed by an operating physician. Without wishing to belimiting, a “proximal end” usually refers to an end closer to thedoctor, and a “distal end” usually refers to an end that enters thepatient first, during normal operation. The terms “axial” and“circumferential” refer to directions respectively along an axis and acircumferential surface of an elastomer.

FIGS. 1 to 3 are schematic diagrams illustrating the structure of anexisting strain gauge. The strain gauge includes three sensitive grids:two longitudinal sensitive grids (the first longitudinal sensitive grid11 and the second longitudinal sensitive grid 12) and one transversesensitive grid (the first transverse sensitive grid 13). The threesensitive grids are electrically interconnected by connections.

Specifically, the first longitudinal sensitive grid 11 includes a firstgrid-like structure 111, a first non-ground interface 112, a groundinterface 113, a ground lead 115 connected to the ground interface 113(this ground lead is a wire connected to one end of the first grid-likestructure 111 by a first connection 116/117) and a first non-ground lead114 connected to the first non-ground interface 112 (the firstnon-ground lead 114 is another wire connected to the other end of thefirst grid-like structure 111).

The second longitudinal sensitive grid 12 includes a second grid-likestructure 121, a second non-ground interface 122, the ground interface113 shared with the first longitudinal sensitive grid 11, the groundlead 115 connected to the ground interface 113 (the ground lead isconnected to one end of the second grid-like structure 121 by a secondconnection 123/125) and a second non-ground lead 124 connected to thesecond non-ground interface 122 (the second non-ground lead 124 isconnected to the other end of the second grid-like structure 121).

The first transverse sensitive grid 13 includes a third grid-likestructure 131, a third non-ground interface 132, the ground interface113 shared with both the first longitudinal sensitive grid 11 and thesecond longitudinal sensitive grid 12, the ground lead 115 connected tothe ground interface 113 and a third non-ground lead 134 connected tothe third non-ground interface 132. The ground lead 115 is connected toone end of the third grid-like structure 131 by part of the firstconnection 116 (as shown in FIG. 1 ) or by part of the second connection125 (as shown in FIG. 2 ), and the third non-ground lead 134 isconnected to the other end of the third grid-like structure 131.

Studies found that, during practical use, the above strain gaugerequires post-calibration of the sensed values and has to be preheatedfor a period of time before it reaches a stable condition that makes itavailable for use. These create inconvenience of use. In order toovercome this, the applicant has conducted extensive research and foundthat the above problems are related to the location where the groundlead extends from.

As can be seen from the figures, in the existing strain gauge, theground lead 115 that is connected to the ground interface 113 extendsfrom the middle between the second longitudinal sensitive grid 12 andthe first transverse sensitive grid 13 (as shown in FIG. 1 ), or fromthe middle between the first longitudinal sensitive grid 11 and thefirst transverse sensitive grid 13 (as shown in FIG. 2 ). This may leadto unequal resistances between the first non-ground interface 112 andthe ground interface 113 and between the second non-ground interface 122and the ground interface 113, which cause the above problem.

Specifically, as shown in FIG. 2 , the resistance R₁₁₂₋₁₁₃ between thefirst non-ground interface 112 and the ground interface 113 is equal toa resistance R₁₁₁ of the first grid-like structure plus a resistanceR₁₁₅ of the ground lead plus a resistance R₁₁₄ of the first non-groundlead and plus a resistance R₁₁₇ of the first connection, and theresistance R₁₂₂₋₁₁₃ between the second non-ground interface 122 and theground interface 113 is equal to a resistance R₁₂₁ of the secondgrid-like structure plus the resistance R₁₁₅ of the ground lead plus aresistance R₁₂₄ of the second non-ground lead plus a resistance R₁₂₅ ofthe second connection. Since the ground interface 113 is a sharedinterface, if it is assumed that the resistance R₁₁₄ of the firstnon-ground lead is equal to the resistance R₁₂₄ of the second non-groundlead, in order to ensure that R₁₁₂₋₁₁₃ is equal to R₁₂₂₋₁₁₃, the sum ofthe resistance R₁₁₁ of the first grid-like structure and the resistanceR₁₁₇ of the first connection should be equal to the sum of theresistance R₁₂₁ of the second grid-like structure and the resistanceR₁₂₅ of the second connection. As the resistance R₁₁₇ of the firstconnection is apparently lower than the resistance R₁₂₅ of the secondconnection, the resistances of the two longitudinal strain-sensitivegrids satisfy R₁₁₁>R₁₂₁, requiring the two longitudinal sensitive gridsto have different wire sizes. As shown in FIG. 3 , the wires andconnections in the existing strain gauge form a Wheatstone bridgecircuit, in which the resistance R₁₂₅ of the second connection isconnected in series individually with each of the resistance R₁₂₁ of thesecond grid-like structure and the resistance R₁₃₁ of the thirdgrid-like structure, and the three are then connected as a whole inparallel with the resistance R₁₁₁ of the first grid-like structure.

Therefore, the existing strain gauge has to be designed with differentwire sizes of the two longitudinal sensitive grids or post-calibrationof output force values. However, both these options involve a complexdesign and inadequate accuracy. Additionally, this strain gauge must bepreheated for 5 to 6 minutes before it becomes stable and available formeasurement. Accordingly, an interventional medical catheter employingthe strain gauge would require an extended period of time for preheatingafter being delivered into the human body. This may impair the use ofthe strain gauge in the interventional medical catheter, increase thecomplexity and risk of an operation procedure to be performed by adoctor, and prolong a patient's suffering.

In view of the above problems of the existing strain gauge, the presentinvention provides a novel strain gauge, which provides higher accuracy,increased stability when connected in a circuit, and improvedinterference rejection performance, dispenses with the need forpost-calibration, and can reach a stable condition in a very short time.When employed in a force sensor or an interventional medical catheter,the strain gauge of the present invention can effectively shorten therequired period of time for preheating the catheter in the human body,reduce the complexity and risk of a surgical procedure to be performedby a doctor, and alleviate a patient's suffering.

As shown in FIGS. 4 to 7 , the strain gauge provided in the presentinvention includes: a substrate 1; one transverse sensitive grid 13arranged on the substrate 1; and two non-transverse sensitive grids botharranged on the substrate 1 so as to be located on opposite sides of thetransverse sensitive grid 13 respectively and both electricallyconnected to the transverse sensitive grid 13.

The two non-transverse sensitive grids are connected to each other bythe transverse connection 210 and share a common ground lead 115 and acommon ground interface 113. One end of the ground lead 115 is connectedto the connection 210 at the middle thereof, and the other end of theground lead 115 is connected to the ground interface 113. The twonon-transverse sensitive grids have equal resistances and are connectedto ends of two non-ground leads having equal resistances, respectively.The other ends of the two non-ground leads are connected to twonon-ground interfaces, respectively.

In the present embodiment, the substrate 1 defines a first direction anda second direction. The first direction is one of a lengthwise directionand a widthwise direction of the substrate, and the second direction isthe other of the lengthwise and widthwise directions.

Preferably, the connection 210 includes a third connection 211 and afourth connection 212, which are joined to and electrically connectedwith each other. The ground lead 115 extends from the junction of thethird connection 211 and the fourth connection 212 (i.e., the middle ofthe connection 210). The third connection 211 has a length that is equalto a length of the fourth connection 212. The transverse sensitive grid13 is electrically connected by the transverse connection 210 to, andshares the common ground lead 115 and the common ground interface 113with, both the two non-transverse sensitive grids. In accordance withthis embodiment of the present invention, sharing the common groundinterface 113 among the three sensitive grids and connecting the groundlead 115 to the middle of the connection 210 ensure that a resistanceR₁₁₂₋₁₁₃ between the first non-ground interface 112 and the groundinterface 113 is equal to a resistance R₁₂₂₋₁₁₃ between the secondnon-ground interface 122 and the ground interface 113. This impartsincreased stability when connected to a circuit and enhancedinterference rejection performance to the strain gauge and enables it toattain a stable condition very rapid, significantly shortening therequired period of time for preheating. Moreover, the strain gauge isrequired to have fewer ground interfaces for connection to a groundinterface of an external power supply, leading to shrinkage of thestrain gauge and hence of a force sensor or interventional medicalcatheter employing the strain gauge. This helps reduce interventionalcost and the risk of patient infection, resulting an increased successrate of interventional treatment. Preferably, according to the presentinvention, both the length and width of the substrate 1 are not morethan 2.0 mm in order to facilitate the strain gauge's attachment to anduse with an interventional medical catheter and enhance itsadaptability.

In this embodiment, the ground lead 115 includes a transverse segment1151 and a longitudinal segment 1152. The transverse segment 1151 isconnected to the connection 210 at the middle thereof, and thelongitudinal segment 1152 is connected to the transverse segment 1151 atone end and to the ground interface 113 at the other end. Specifically,the transverse segment 1151 is arranged in parallel to transverse wiresegments in the transverse sensitive grid 13, while the longitudinalsegment 1152 is arranged to be perpendicular to the transverse wiresegments in the transverse sensitive grid 13. This design avoidsdislocation of the transverse sensitive grid 13 and retains it around acenter of the strain gauge. In this way, the various interfaces of thestrain gauge are spaced apart by proper distances, which avoidshort-circuiting during welding

Additionally, in this embodiment, the transverse wire segments in thetransverse sensitive grid 13 are connected to the connection 210 in thevicinity of the middle thereof. This allows the transverse sensitivegrid 13 to become stable at a same time as that of the non-transversesensitive grids, thus additionally improving the strain gauge'sperformance during use.

As shown in FIGS. 4 to 5 , in an embodiment of the present invention,the two non-transverse sensitive grids are longitudinal sensitive grids(i.e., a first longitudinal sensitive grid 11 and a second longitudinalsensitive grid 12). The first longitudinal sensitive grid 11 and thesecond longitudinal sensitive grid 12 may be implemented as beingarranged side by side and aligned with each other along the firstdirection (i.e., longitudinal wire segments therein extend in the firstdirection), with the transverse sensitive grid 13 being disposedtherebetween. The transverse sensitive grid 13 is arranged along thesecond direction (i.e., the transverse wire segments therein extend inthis direction). Grid widths of the two longitudinal sensitive grids 11,12 may be aligned with a grid length of the transverse sensitive grid13. Alternatively, grid lengths of the two longitudinal sensitive grids11, 12 may be aligned with a grid width of the transverse sensitive grid13.

In this embodiment, a resistance R₁₁₂₋₁₁₃ between the first non-groundinterface 112 and the ground interface 113 of the strain gauge is equalto a resistance R₁₁₁ of the first grid-like structure plus a resistanceR₁₁₅ of the ground lead plus a resistance R₁₁₄ of the first non-groundlead plus a resistance R₂₁₁ of the third connection, and a resistanceR₁₂₂₋₁₁₃ between the second non-ground interface 122 and the groundinterface 113 is equal to a resistance R₁₂₁ of the second grid-likestructure plus the resistance R₁₁₅ of the ground lead plus a resistanceR₁₂₄ of the second non-ground lead plus a resistance R₂₁₂ of the fourthconnection. The applicant has found from research that the resistancesof the connections depend on the location where the ground lead extendsfrom. According to embodiments of the present invention, connecting theground lead 115 to the middle of the connection 210 can ensure that theleft and right connections, i.e., the third connection 211 and thefourth connection 212 have the same length and resistance. In this way,when the wire resistance of the first longitudinal strain sensitive grid11 is equal to that of the second longitudinal strain sensitive grid 12,i.e., the resistance R₁₁₁ of the first grid-like structure is equal tothe resistance R₁₂₁ of the second grid-like structure, the resistanceR₁₁₂₋₁₁₃ between the first non-ground interface 112 and the groundinterface 113 will be equal to the resistance R₁₂₂₋₁₁₃ between thesecond non-ground interface 122 and the ground interface 113. This canresult in increased accuracy, high stability when connected in acircuit, a shorter period of time for preheating taken to attain astable condition (in only 2-3 seconds in the present embodiment, ascompared to in 5-6 minutes for the existing strain gauge) and enhancedinterference rejection performance of the strain gauge.

Preferably, in this embodiment, the grid width of each sensitive grid inthe strain gauge is equal to the grid length thereof, and the grid-likestructures of the sensitive grids are all identical. In addition, oneend of the transverse sensitive grid 13 is connected to the connection210, and the other end of the transverse sensitive grid 13 is connectedto the third non-ground lead 134. The third non-ground lead 134, thefirst non-ground lead 114 and the second non-ground lead 124 have equalresistances, and the third non-ground lead 134 is connected to the thirdnon-ground interface 132. This enables the strain gauge to have a morecompact and more stable structure.

Considering that, in some cases, strain may occur not along thedirection of a center axis of the strain gauge but along a directioninclined therefrom at an angle of even possibly up to 90 degrees (e.g.,under the action of a force along a radial direction (i.e., a transverseforce)), as shown in FIGS. 6 to 7 , in another embodiment of the presentinvention, the two non-transverse sensitive grids (i.e., the firstnon-transverse sensitive grid 14 and the second non-transverse sensitivegrid 15) are arranged in symmetry and oriented at a predetermined anglewith respect to the first direction, with the transverse sensitive grid13 being arranged along the second direction. This arrangement enablesboth axial and transverse strain measurement of the strain gauge,expanding its scope of application.

Preferably, in this embodiment, in addition to the above describedstructural details of the strain gauge, the wires in the left and rightnon-transverse sensitive grids may be deflected by an angle in order toaddress biaxial stress measurement and analysis in cases with thedirections of the principal axes remaining unknown. Preferably, thewires are deflected by 45° (i.e., forming an angle of 45° with the firstdirection). This enables the strain gauge to address the measurement ofunknown stresses as many as possible and to monitor forces from variousdirections, thereby providing a doctor with more accurate stressdirection information.

In this embodiment, a resistance R₁₄₁₋₁₁₃ between the non-groundinterface 141 of the first non-transverse sensitive grid 14 and theground interface 113 is equal to a resistance R₁₄₃ of the grid-likestructure of the first non-transverse sensitive grid plus the resistanceR₁₁₅ of the ground lead plus a resistance R₁₄₅ of the non-ground lead ofthe first non-transverse sensitive grid plus the resistance R₂₁₁ of thethird connection, and a resistance R₁₅₁₋₁₁₃ between the non-groundinterface 151 of the second non-transverse sensitive grid 15 and theground interface 113 is equal to a resistance R₁₅₃ of the grid-likestructure of the second non-transverse sensitive grid plus theresistance R₁₁₅ of the ground lead plus a resistance R₁₅₅ of thenon-ground lead of the second non-transverse sensitive grid plus theresistance R₂₁₂ of the fourth connection.

In this embodiment, the ground lead 115 of the ground interface 113 alsoextends from the middle of the connection 210, allowing the left andright connections, i.e., the third connection 211 and the fourthconnection 212, to have the same length and resistance. As such, theresistance R₁₄₁₋₁₁₃ between the first non-ground interface 141 and theground interface 113 is equal to the resistance R₁₅₁₋₁₁₃ between thesecond non-ground interface 151 and the ground interface 113. Thisallows increased accuracy, a shorter period of time for preheating andenhanced stability when connected in a circuit of the strain gauge.

In other embodiments, a plurality of, e.g., 4 or 6, pairs ofnon-transverse sensitive grids may be arranged on the substrate. Thenon-transverse sensitive grids in each pair may be arranged in symmetrywith respect to the transverse sensitive grid so that the twonon-transverse sensitive grids on opposite sides of the transversesensitive grid are spaced apart therefrom by equal distances and havesame resistances. The non-transverse sensitive grids are connected tothe transverse sensitive grid by transverse connections and share acommon ground lead and a common ground interface with the transversesensitive grid. In such embodiments, the same technique effects can beobtained, and the present invention is not limited in any sense in thisregard.

According to the present invention, the substrate 1 is a semi-rigidsubstrate. Preferably, the substrate 1 is made of a semi-rigid plasticmaterial. For example, the material of the substrate 1 is one selectedfrom the special polymer materials polyimide (PI) andpolyetheretherketone (PEEK), or a combination thereof. More preferably,the substrate 1 is fabricated from a PEEK material, which can impartboth excellent rigidity and flexibility to the substrate 1.

The present invention also provides a force sensor 20, which includes,as shown in FIG. 8 , an elastomer 21 and strain gauges 10 according toany of the foregoing embodiments. The strain gauges 10 are arranged onthe elastomer 21. Preferably, in this embodiment, the elastomer 21 is acylindrical hollow elastomer.

In this embodiment, the elastomer 21 preferably has at least twocircumferentially extending through-slots 22. Preferably, betweenopposite ends of each through-slot 22, one of the strain gauges 10 isarranged. The through-slots 22 are formed in different circumferentialplanes and staggered from each other circumferentially (i.e., they arestaggered from each other both axially and circumferentially)

In this embodiment, an axial slot 23 is provided at each of the oppositeends of each through-slot 22. Preferably, the axial slot 23 extendsalong an axis of the elastomer 21 over a length not less than the gridwidths or grid lengths of the sensitive grids in the strain gauges, ornot less than an axial width of the sensitive grids on the axis of theelastomer 21. Since the grid-like structures of the strain gauges 10will be subjected to the greatest strain at their portions around theaxial slots 23, the above length design allows the axial slots 23 toprovide indications that can guide the strain gauges 10 to be attachedto the most stressed locations. This enables the strain gauges 10 tooutput stronger signals, from which better measurements can be obtained.

Specifically, as shown in FIGS. 9 to 10 , in this embodiment, the forcesensor includes an elastomer 21 and at least two strain gauges 10, whichare provided on an external surface of the elastomer 21 in order tomeasure axial and circumferential strain at at least two differentlocations of the elastomer 21. The at least two strain gauges 10 areprovided in different circumferential planes and staggered from eachother circumferentially Orthographic projections of the two straingauges 10 on a cross section of the elastomer 21 are preferably evenlydistributed around the circumference of the elastomer 21.

In this embodiment, two strain gauges, i.e., a first strain gauge and asecond strain gauge, are provided, for example. The first strain gaugeincludes one substrate, two non-transverse sensitive grids and onetransverse sensitive grid. The two non-transverse sensitive grids arearranged in symmetry and each along a direction inclined from the axisof the elastomer at a predetermined angle (preferably of 45°). Thetransverse sensitive grid between the two non-transverse sensitive gridsis arranged along the circumference of the elastomer. The second straingauge includes another substrate, two longitudinal sensitive grids andone transverse sensitive grid. The two longitudinal sensitive grids arearranged side by side and aligned with each other along the axis of theelastomer. The transverse sensitive grid between the two longitudinalsensitive grids is arranged along the circumference of the elastomer.

In practical implementations, the two strain gauges 10 attached to theelastomer 21 may be two first strain gauges, or two second straingauges, or a combination of one first strain gauge and one second straingauge (i.e., the two strain gauges 10 may be identical or not). In thisembodiment, the two strain gauges are capable of sensing strain at twodifferent locations of the elastomer 21, ensuring that practical contactforce measurement needs can be satisfied. The design with the two straingauges allows a shorter axial length of the elastomer 21 and hence of aninterventional medical catheter employing the force sensor, resulting incost savings.

The present invention also provides an interventional medical catheterincluding a distal catheter end where the force sensor 20 according toany of the above embodiments is provided. The interventional medicalcatheter further includes an electrode 30 attached to the force sensor20, as shown in FIGS. 8 to 11 . In this embodiment, the force sensor 20includes the above described two strain gauges for sensing strainsignals.

In summary, in the strain gauge, force sensor and interventional medicalcatheter provided in the present invention, the shared ground leadextends from the middle of the connection in the strain gauge, which canensure that the wires in the left and right strain sensitive grids havethe same size and resistance and impart higher stability when connectedin a circuit and enhanced interference rejection performance to thestrain gauge. Through employing the strain gauge in the force sensor andthe interventional catheter, the catheter's required period of time forpreheating in the human body can be effectively shortened, and thecomplexity and risk of an operation procedure to be performed by adoctor and a patient's suffering can be reduced. Further, thecompactness of the strain gauge of the present invention allows ashorter length of the elastomer in the force sensor and shrinkage of theinterventional medical catheter, resulting in cost savings.

The various technical features of the foregoing embodiments may becombined in any way. Although not all such combinations have beendescribed above for the sake of brevity, any of them is considered tofall within the scope of this specification as long as there is nocontradiction between the technical features.

Presented above are merely several embodiments of the presentapplication. Although these embodiments are described with someparticularity and in some detail, it should not be construed that theylimit the scope of the present application in any sense. Note thatvarious variations and modifications can be made by those of ordinaryskill in the art without departing from the concept of the presentapplication. Accordingly, it is intended that all such variations andmodifications are embraced within the scope of this application asdefined in the appended claims

1. A strain gauge, comprising: a substrate; a transverse sensitive grid, arranged on the substrate; and at least two non-transverse sensitive grids, both arranged on the substrate so as to be located on opposite sides of the transverse sensitive grid and both electrically connected to the transverse sensitive grid, wherein the two non-transverse sensitive grids are connected to each other by a transverse connection and share a common ground lead and a common ground interface, one end of the ground lead connected to the transverse connection at a middle thereof, the other end of the ground lead connected to the ground interface, the two non-transverse sensitive grids having equal resistances and connected to ends of two respective non-ground leads having equal resistances, the other ends of the two non-ground leads connected to two respective non-ground interfaces.
 2. The strain gauge according to claim 1, wherein the substrate defines a first direction and a second direction, the first direction being one of a lengthwise direction and a widthwise direction of the substrate, the second direction being the other of the lengthwise and widthwise directions of the substrate.
 3. The strain gauge according to claim 2, wherein the two non-transverse sensitive grids are arranged in symmetry and each long a direction inclined from the first direction at a predetermined angle, with the transverse sensitive grid being arranged along the second direction.
 4. The strain gauge according to claim 2, wherein the two non-transverse sensitive grids are longitudinal sensitive grids which are arranged side by side and aligned with each other along the first direction, with the transverse sensitive grid being arranged along the second direction, and wherein grid widths of the longitudinal sensitive grids are aligned with a grid length of the transverse sensitive grid, or grid lengths of the longitudinal sensitive grids are aligned with a grid width of the transverse sensitive grid.
 5. The strain gauge according to claim 1, wherein a grid width of each of the sensitive grids is equal to a grid length thereof, and wherein grid-like structures in the sensitive grids are all identical.
 6. The strain gauge according to claim 1, wherein the transverse sensitive grid is electrically connected to the two non-transverse sensitive grids through the transverse connection, and wherein the transverse sensitive grid and the two non-transverse sensitive grids share the common ground lead and the common ground interface.
 7. The strain gauge according to claim 6, wherein the transverse sensitive grid comprises transverse wire segments which are connected to the transverse connection at a location close to the middle of the transverse connection.
 8. The strain gauge according to claim 1, wherein the ground lead comprises a transverse segment and a longitudinal segment, the transverse segment connected to the transverse connection at the middle thereof, the longitudinal segment connected to the transverse segment at one end and to the ground interface at the other end.
 9. The strain gauge according to claim 8, wherein the transverse sensitive grid comprises a transverse wire segment arranged in parallel to the transverse segment and perpendicular to the longitudinal segment.
 10. The strain gauge according to claim 1, wherein the two non-transverse sensitive grids include a first non-transverse sensitive grid and a second non-transverse sensitive grid, which are connected to a first non-ground lead and a second non-ground lead, respectively, and wherein one end of the transverse sensitive grid is connected to the transverse connection, and the other end of the transverse sensitive grid is connected to a third non-ground lead, the first, second and third non-ground leads having equal resistances, the third non-ground lead connected to a third non-ground interface.
 11. A force sensor, comprising an elastomer and strain gauges as defined in claim 1, wherein the strain gauges are provided on the elastomer.
 12. The force sensor according to claim 11, wherein the elastomer is provided therein with a plurality of through-slots extending circumferentially around the elastomer, each of the through-slots provided at each of opposite ends thereof with an axial slot extending along an axis of the elastomer.
 13. The force sensor according to claim 12, wherein the axial slots each have a length that is not less than a grid width or grid length of each sensitive grid in each strain gauge, or not less than a width of each sensitive grid along the axial of the elastomer.
 14. An interventional medical catheter, comprising a distal catheter end provided thereon with a force sensor as defined in claim
 11. 